People vary in their level of fitness, and opinions about what it means to be physically fit can diverge widely as well. A 60-year-old man who does moderate, low-intensity exercise four times a week might feel he's very physically fit compared to everyone else his age, but a 22-year-old woman engaging in the same fitness routine might not be considered superbly fit by anyone's standards.

Still, it is incredibly hard to pinpoint how well you are doing physically compared to other people your age because fitness can be hard to quantify. Sure, you can track your minutes per mile, your number of pushups or your length of time on the elliptical each day, but these numbers means little from person-to-person because we differ on metabolism, height, weight, health issues and needs.

But researchers at the Norwegian University of Science and Technology have come up with an easy algorithm to measure one's "fitness age" – or, as a recent New York Times article puts it, "how well your body functions physically, relative to how well it should work, given your age." Previously, these numbers would be determined in an exercise-physiology lab. However, the Norwegian researchers found a way to come up with someone's VO2 max levels – the peak oxygen intake, which measures how well our bodies get oxygen to the cells. VO2 max can tell someone's fitness age.

The researchers took resting heart rate, HDL cholesterol and total cholesterol levels, body mass index, height and resting heart rate. Then, they had each person run on a treadmill until they were completely exhausted in order to determine VO2. If you're interested in learning your fitness age, try out the university's VO2 calculator for quick, accurate results.

The good thing about learning your fitness age is that if it is older than your actual age, you can make some easy adjustments – such as working out more frequently – to lower it.